| OCR Text |
Show Fenimore Mechanism The formation of HCN via CH reaction with NO was discussed in the previous section. Another step which yields HCN is the reaction between CH and molecular nitrogen; i.e., the Fenimore mechanism: - ...~ HCN + N The nitrogen which contributes to the Fenimore mechanism could come from p ri rna ry combust ion ai r, burnout ai r, or reburni ng fuel di 1 uent. Thi s mechanism, which causes the formation of thermal NOx, occurs most readily at high temperatures. Tests were completed with nitrogen dilution of the reburning gas, and a nitrogen-free primary zone oxidant composed of argon, oxygen, and carbon dioxide. The results are presented in Figure 6. The data showed that the primary zone nitrogen did not contribute to the Fenimore mechanism in the reburning zone. A slight increase in NOx emissions was observed when the argon diluent was replaced by nitrogen. The results implied that the Fenimore mechanism was not important in the reburning process. Reburning Temperature The results discussed above were obtained with the reburning fuel injected at 25500F. A series of experiments were carried out to investigate the influence of temperature on rich zone NO reduction. The reburning fuel was injected at temperatures ranging from 25500F to 1600oF. At the optimum stoichiometry of 0.9, the concentrations of NO were measured at 400 ms downstream of the reburning fuel injection location. Figure 7 presents these data and indicates that the NO reduction efficiency in the reburning zone decreased with temperature, with NO concentration measured at 2550 0F approximately half of that seen at 1800 0 F. However, the effect of temperature diminished when the reburning fuel was injected above 22000 F. It is believed that the formation of thermal NO would become important at temperatures above 26000F. 5 |
